1. Field of the Invention:
The present invention relates to the formation of thin film capacitors and more particularly to the formation of thin film capacitors on a ceramic substrate.
2. Description of the Prior Art:
It is desirable to place thin film capacitors on ceramic substrates particularly multilevel ceramic substrates having through vias. It is highly desirable to provide low inductance and low parasitic decoupling capacitance at the chip interconnection points. Ideally this capacitor should be joined to the substrate below and to an integrated circuit chip on top. This joining may be by controlled collapsed chip connections or other techniques.
Typical thin film process steps include a platinum electrode deposition followed by sputtered dielectric deposition on a ceramic base substrate. The sputtered dielectric film is often very thin, about 3,000 A and it is intrinsically highly stressed. In combination with imperfections on this ceramic surface, this leads to electrical shorts in the formed thin film capacitors. Techniques to improve the thin film capacitor are related to 1) improving the surface characteristics of the ceramic surface to the point where the overlying thin films are deposited in a perfectly smooth manner without imperfections; or 2) to make thin film structure robust enough to handle a certain level of defects in the ceramic yet stay free of electrical shorts.
To aid in manufacturability with low cost, it is desirable to form the thin film capacitor by placing it directly on a substrate with high yield and with high capacitance.
The present invention uses a unique thin film metallization scheme on ceramic following by in situ oxidation to create a metal oxide capacitor. The combination of metals when used with the appropriate optimized oxidation conditions ensures a high yield of good capacitors each having high capacitance value.
The process is to deposit an adhesion layer followed by a metal electrode which is followed by a diffusion barrier, then a dielectric material. A top electrode is formed to complete the capacitor.
In one embodiment, a dielectric material may be deposited on the diffusion barrier or in a second embodiment, the dielectric material may be formed by oxidation of a metal placed on top of the diffusion barrier which provides a self-healing of any pin holes within the dielectric material to prevent electrical shorts.